1. FIELD OF THE INVENTION:
The present invention relates to a novel process for producing 2-chloro-5-trichloromethyl pyridine by reacting .beta.-picoline with chlorine in a gaseous phase. 2-Chloro-5-trichloromethyl pyridine is useful as an intermediate for medicines, agricultural chemicals and dyes especially herbicides.
2. DESCRIPTION OF THE PRIOR ARTS:
It has been proposed to produce 2-chloro-5-trichloromethyl pyridine by diazotizing 2-amino-5-methyl pyridine and then brominating it to obtain 2-bromo-5-methyl pyridine and dissolving it in carbon tetrachloride and chlorinating it with chlorine in a liquid phase under irradiating ultraviolet rays.
However, this process has disadvantages that 2-amino-5-methyl pyridine as the starting material is expensive and complicated reaction steps are required and a reaction time is long.
The inventors have considered to carry out a gas phase chlorination of .beta.-picoline as an economical starting material. However, it has been considered to be difficult to succeed in a chlorination of .beta.-picoline so as to convert methyl group at .beta.-position to trichloromethyl group, more difficult to succeed in a chlorination of .beta.-picoline to di- or tri-chloromethyl group than monochloromethylation. Thus, an industrial success has not been expected.
For example, in HELVETICA CHIMICA ACTA, Vol. 59, Fase 1, Nr. 19-20, 1976 there is the description that the chlorination of methyl group of .beta.-picoline is difficult, and 2,6-dichloro-3-halogenated methyl pyridine can be obtained from .alpha.-methylene glutaronitrile. In U.S. Pat. No. 3,412,095, there is the description that .beta.-picoline is chlorinated in a gaseous phase in the presence of steam to obtain monochloromethyl compound, however there is no description that trichloromethyl compound is obtained. Even though the chlorination is further carried out by increasing proportion of chlorine by this process, only nicotinic acid is obtained. It has been proposed to produce 2-chloro-5-trichloromethyl pyridine by dissolving .beta.-picoline in carbon tetrachloride and introducing chlorine gas in the solution under irradiating ultraviolet rays. However, the reaction time is too long and the yield is too low as several percent and this is not suitable for industrial purpose.